[AMDGPU] SIWholeQuadMode: don't add duplicate implicit $exec operands

[foad]

Summary

STRICT_WWM and STRICT_WQM are already defined with Uses = [EXEC], so
there is no need to add another implicit use of $exec when lowering them
to V_MOV_B32 instructions.

[critson]

LGTM

I think this particular line of code is pretty old.
I take it this is largely NFC on compiler output (i.e. no test difference)?

[foad]

In D100969#2706882, @critson wrote:

I take it this is largely NFC on compiler output (i.e. no test difference)?

Yes it just affects the MIR, but there are no explicit tests for that.

llvm/lib/Target/AMDGPU/SIWholeQuadMode.cpp

if (TRI->isVGPR(*MRI, Reg)) {
       const TargetRegisterClass *regClass =
           Reg.isVirtual() ? MRI->getRegClass(Reg) : TRI->getPhysRegClass(Reg);
       if (SubReg)
         regClass = TRI->getSubRegClass(regClass, SubReg);
 
       const unsigned MovOp = TII->getMovOpcode(regClass);
       MI->setDesc(TII->get(MovOp));
 
-      // And make it implicitly depend on exec (like all VALU movs should do).
-      MI->addOperand(MachineOperand::CreateReg(AMDGPU::EXEC, false, true));
+      // Check that it already implicitly depends on exec (like all VALU movs
+      // should do).
+      assert(any_of(MI->implicit_operands(), [](const MachineOperand &MO) {
+        return MO.isUse() && MO.getReg() == AMDGPU::EXEC;
+      }));
     } else {
       // Remove early-clobber and exec dependency from simple SGPR copies.
       // This allows some to be eliminated during/post RA.
       LLVM_DEBUG(dbgs() << "simplify SGPR copy: " << *MI);
       if (MI->getOperand(0).isEarlyClobber()) {
         LIS->removeInterval(Reg);
         MI->getOperand(0).setIsEarlyClobber(false);
         LIS->createAndComputeVirtRegInterval(Reg);